1. Field of the Invention
The present invention relates to a device for reducing power consumption in medical electrical equipment, implantable in the human body of the type having a sensor, composed of a sensor element and sensor electronic circuitry, to sense a parameter, relevant to control of the equipment's in vivo operation, and a comparator for comparing the sensor's output signal to a predesignated threshold value.
2. Description of the Prior Art
In recent years, technicians have succeeded in making a drastic reduction in the power consumed by electrical equipment implantable in the human body. In the case of pacemakers, for example, stimulation current has been reduced from 5-10 .mu.A to 0.5-2 .mu.A, and the internal power consumption of pacemaker electronics has been reduced from, typically, 10 .mu.A to, typically, 3.5 .mu.A.
European Application 0 191 404 describes a dual sensor system for pacemaker control, having a sensor for sensing physical activity and a sensor for sensing a physiological parameter in the patient, such as partial oxygen pressure. The activity sensor is a passive element which does not require any power for operation. The electrically powered physiological sensor is only activated when the activity sensor senses physical activity by the patient above a predesignated threshold value. Thus the electrically powered physiological sensor is only in operation at times when sensing of the relevant physiological parameter is of interest, resulting in an attendant saving in energy.
An operation amplifier, which is automatically switchable between a "sleep mode", when the input signal is less than a predesignated threshold value, and an "awake mode", when the input signal exceeds the threshold value, is described in Motorola Semiconductor Technical Data Sheet MC 33102 "Sleep-Mode Two-State, Micropower Operational Amplifier," Motorola Literature Distribution, Arizona, USA, 1991. However, power consumption is still as high as about 50 .mu.A even in the sleep mode.